The dinoflagellate Alexandrium catenella producing only carbamate toxins may account for the seafood poisonings in Qinhuangdao, China

•We retrieved causative agents of seafood poisonings in Qinhuangdao via several ways.•High throughput sequencing data revealed 3 toxic species within genus Alexandrium.•Germination of Alexandrium cyst in sediment led to 3 toxic isolates of A. catenella.•All isolates produce only carbamate toxins which were major toxins in phytoplankton.•The results suggest A. catenella is most likely the causative agent of poisonings.